This invention pertains to controls for variable displacement motors utilizing a motor speed sensitive signal to vary motor displacement whereby motor displacement decreases as output speed increases and, in a normal driving range as when a motor is used in a vehicle drive, this allows vehicle speed to be controlled by the pump displacement as motor speed is a positive function of motor flow. This allows the normal pump control to function independently of the motor to achieve vehicle speed without interconnecting signal lines to the motor control.
Additionally, the invention pertains to systems using the aforesaid motor control in vehicle drives having plural motors to provide improved anti-slip control, to achieve load compensation when a load shifts due to acceleration or deceleration and allow wheel torque shift to match the vehicle weight shift due to the acceleration or deceleration and to provide for steer compensation whereby the torque applied to the wheels or other traction device at the sides of the vehicle may be varied to assist the geometry of the vehicle turn.
It is known in the prior art to utilize a motor speed sensitive signal to control the displacement of a variable displacement motor as shown in the Tomlinson U.S. Pat. No. 2,518,578. The motor control shown in said patent does not show a system wherein the motor can go to zero displacement nor does it show various ways wherein the speed signal can be varied or modified for desired operations. The Tomlinson patent discloses plural wheel drive motors driven by one pump. However, there is no disclosure of controlling slip of one of the driven wheels and the disclosed motor control does not permit moving the motor to zero displacement. The control of the patent does not limit motor flow and, therefore, cannot limit motor speed to provide good operation under wheel spin-out conditions.
In addition to the aforesaid patent, it is known to have multiple motor drive systems driven by one pump whereupon if one of the wheels has poor traction, there would be a tendency for the wheel speed and associated motor speed to increase and, in fact, overspeed. Such systems have used flow control valves in the motor line to limit flow to a slipping motor and resultingly limit motor speed.
The Anderson U.S. Pat. Nos. 3,177,964 and 3,199,286, disclose multiple motor systems driven by one pump wherein each of the motors has variable displacement. In the first patent, displacement of a motor is varied in response to the actual torque and weight forces sensed by sensing mechanism associated with the vehicle wheel and motor system. The patent describes this system as modifying the displacement of the stroke of a motor associated with a slipping vehicle wheel.
The second Anderson patent discloses plural variable displacement motors which have their displacement varied in response to system pressure whereby, as system pressure goes up, the displacement of the motors increases until a maximum displacement position is reached. This patent does not disclose any system for sensing system pressure for load-compensation or steer-compensation for the motors.